In the hydrocarbon extraction industry categories of contaminated water requiring treatment include surface wastewater; originating from precipitation and groundwater sources, produced water; recovered from underground with associated hydrocarbons, and process water; introduced during hydrocarbon production techniques. Hydrocarbon production techniques which use large quantities of water include; Cyclic Steam Stimulation (CSS) for heavy oil production, Steam Assisted Gravity Drainage (SAGD) for oilsand bitumen production, Water Flooding for conventional oil reservoir production and hydraulic fracturing for unconventional gas and oil production. These forms of wastewater typically include a number of individual components namely, water, hydrocarbons, suspended solids, and contaminants which include but are not limited to, dissolved solids, naturally occurring compounds and synthetic additives.
Current industrial practices include disposing of contaminated wastewater into deep underground disposal wells, impoundment and various treatment technologies. Compliance with increasingly stringent environmental regulations requires improved processes to separate and extract the hydrocarbons, solids and contaminants and process the water to a purity suitable for re-use for industrial purposes, or potentially to a significantly enhanced purity suitable for re-use for agricultural purposes or environmentally sustainable discharge.
Various surfactants, filters and chemical additives have been developed for extracting hydrocarbons from wastewater. One example is membrane bioreactors which have been also proposed for use in hydrocarbon removal from industrial wastewater. In the known arrangements, the reactors employ hollow fibre membranes. The reactors typically employ microfiltration hollow fibres which are submerged in the bioreactor.
In U.S. Pat. No. 6,521,125, there is disclosed an oil/hydrocarbon removal system. It is indicated in the disclosure that the system is useful for collecting the bilge of marine vessels which assists in ensuring that there is oil-free water in the surrounding water of the vessels. The filter in the medium is indicated to comprise a mixture of peat, anthracite and bentonite to produce a composition that is both hydrophobic and oleophilic.
In many instances, in the individual arrangements discussed above, the filter technology requires the replacement of the filter material which is eventually prone to plugging and general wear or reduced effectiveness. This presents difficulties in a remote location where accessibility of replacement parts is challenging, if not impossible. Further, many of the technologies are particularly effective as filters for removing the hydrocarbons, however, in many situations the water which must be discharged or otherwise handled is not properly decontaminated in compliance with stringent environmental restrictions.
Particularly in the case of produced water, there are typically high levels of dissolved solids and salts, and therefore desalination treatment may also be required prior to re-use or discharge.
Reverse osmosis membranes are the most prevalent desalination treatment for large volumes of water. However, even minimal levels of hydrocarbons in the input fluid stream will cause fouling, resulting in impaired functionality and deterioration or irreversible damage to the membranes. The presence of suspended solids and contaminants such as iron and calcium, cause scaling and deposits which impair functionality and require periodic cleaning with harsh chemicals, resulting in interrupted processing and a reduced membrane lifecycle.
Therefore, utilization of membrane filtration treatment processes such as reverse osmosis membranes for streams of fluid containing hydrocarbons, requires preliminary treatment to remove hydrocarbons, solids and scaling and deposit contaminants from the stream of fluid before it encounters the membrane. A prevalent preliminary treatment approach is ceramic membrane ultra-filtration. However, ceramic membranes require frequent backwash cleaning cycles to remove trapped hydrocarbons, solids and contaminants. Cleaning periodically interrupts processing. It also generates a backwash fluid waste stream which requires disposal. Costs include backwash fluid waste disposal services, a supply of hazardous cleaning chemicals and a dependency upon expensive consumable replacement membranes.
A need therefore exists, for a cost-effective preliminary treatment which enables effective utilisation of auxiliary treatment methods such as reverse osmosis membranes.
Surface wastewater generated in hydrocarbon extraction industry activities may become contaminated with drilling mud, hydrocarbons and chemicals. Current industry management practices include transportation and disposal into an injection well or use of a boiler to evaporate contaminated surface wastewater. Boiler evaporation is environmentally undesirable because the contaminants in untreated water are also discharged into the atmosphere. Additionally significant quantities of diesel fuel are consumed to heat the boiler, particularly during winter drilling activities when the volume of diesel fuel consumed may be equivalent to the volume of water to be evaporated.
There is therefore an increasing industrial need for effective, economically viable and environmentally sustainable processes for enabling the treatment, and re-use or discharge, of wastewater containing hydrocarbons, suspended solids, and contaminants which include but are not limited to dissolved solids, naturally occurring compounds and synthetic additives.